The present invention relates to disc drives. More particularly, the present invention relates to a servo positioning system in a disc drive.
A typical disc drive includes one or more magnetic discs mounted for rotation on a hub or spindle. A typical disc drive also includes a transducer supported by a hydrodynamic air bearing which flies above each magnetic disc. The transducer and the hydrodynamic air bearing are collectively referred to as a data head. A drive controller is conventionally used for controlling the disc drive based on commands received from a host system. The drive controller controls the disc drive to retrieve information from the magnetic discs and to store information on the magnetic discs.
An electromechanical actuator operates within a negative feedback, closed-loop servo system. The actuator moves the data head radially over the disc surface for track seek operations and holds the transducer directly over a track on the disc surface for track following operations.
Information is typically stored in concentric tracks on the surface of the magnetic discs by providing a write signal to the data head to encode flux reversals on the surface of the magnetic disc representing the data to be stored. In retrieving data from the disc, the drive controller controls the electromechanical actuator so that the data head flies above the magnetic disc, sensing the flux reversals on the magnetic disc, and generating a read signal based on those flux reversals. The read signal is typically conditioned and then decoded by the drive controller to recover data represented by flux reversals stored on the magnetic disc, and consequently represented in the read signal provided by the data head.
In an embedded servo-type system, servo information is recorded on tracks which also contain data stored on the disc drive. The servo data (or servo bursts) are written on the data tracks and are commonly evenly temporally spaced about the circumference of each track. Data to be stored on the disc drive is written between the servo bursts.
As a transducer reads the servo information, the transducer provides a position signal which is decoded by a position demodulator and presented in digital form to a servo control processor. The servo control processor essentially compares actual radial position of the transducer over the disc (as indicated by the embedded servo burst) with desired position and commands the actuator to move in order to minimize position error.
In the past, dedicated servo-type systems were used. In a dedicated servo system, an entire disc surface in a disc drive was dedicated to servo information. Thus, high sample rates from the servo information could be maintained. However, in order to increase disc storage capacity, the above-described embedded (or sectored) servo systems are used. One disadvantage of this type of system is that, since data is also stored on the tracks containing servo information, the sample rate obtainable for servo information is lower than with a dedicated servo system. As the sample rate of the servo position information decreases, certain performance limitations increase.
A servo system positions a transducer over a disc surface in a disc drive system. Disc surfaces in the drive each have a plurality of spaced servo samples recorded thereon. The servo samples on at least two of the disc surfaces are recorded in skewed relation to one another. A plurality of transducers are provided and one transducer is associated with each one of the plurality of disc surfaces. An actuator arm assembly is coupled to the transducers to move the transducers relative to the disc surfaces. A servo control system is coupled to the actuator arm assembly to control position of the actuator arm assembly. The servo control system includes a reader configured to read servo samples from at least two disc surfaces such that at least two servo samples are read within one servo time period.